Back in January 2010, the Bulletin of the Atomic Scientists announced that they were moving their "Doomsday Clock" from five to six minutes to midnight, a sign of cautious optimism and renewed hope for Earth's nuclear safety.

Yeah, about that...

This symbolic clock was introduced back in 1947 as a way for atomic scientists to illustrate the imminent danger of nuclear weapons. The clock was initially set at 7 minutes to midnight - midnight, of course, representing the annihilation of humanity - and got all the way down to two minutes to midnight at the height of the Cold War. The breakup of the Soviet Union pushed it all the way back to 17 minutes to midnight, but it's been ticking closer ever since with renewed threats to the planet's security, primarily in the form of nuclear and biological weapon proliferation and global warming. Now, after a couple years of being six minutes to midnight, we're officially back down to five minutes away.

In an official statement, the Bulletin of Atomic Scientists explained their decision:

"It is five minutes to midnight. Two years ago, it appeared that world leaders might address the truly global threats that we face. In many cases, that trend has not continued or been reversed. For that reason, the Bulletin of the Atomic Scientists is moving the clock hand one minute closer to midnight, back to its time in 2007."

The complete statement cites a number of factors in the decision, including the lack of progress in international agreements on topics such as the climate and nuclear power and weapons. The Fukushima nuclear disaster also weighed heavily on the decision, as did recent efforts by Indonesia, Turkey, and the United Arab Emirates to gain nuclear power. In the statement, BAS member Lawrence Krauss expanded on the renewed pessimism that led to the change in the Doomsday clock:

"Faced with clear and present dangers of nuclear proliferation and climate change, and the need to find sustainable and safe sources of energy, world leads are failing to change business as usual. Inaction on key issues including climate change, and rising international tensions motivate the movement of the clock. As we see it, the major challenge at the heart of humanity's survival in the 21stcentury is how to meet energy needs for economic growth in developing and industrial countries without further damaging the climate, exposing people toloss of health and community, and without risking further spread of nuclear weapons, and in fact setting the stage for global reductions."